It will be appreciated that in electronic warfare, and more particularly for infrared missile countermeasures, pulsed waveforms are employed that are used to illuminate a missile seeker to countermeasure the incoming missile. This is accomplished by injecting the waveforms into the seeker that will confuse the seeker or cause it to guide the missile wave from its intended target.
There is therefore a need to be able to produce a pulsed waveform with predetermined variable pulse widths and to do so over the entire engagement that can be as long as twenty seconds. Note the pulse widths must be controlled to vary pulse by pulse so that different pulse widths are generated for the entire engagement period without having to replicate the same train pulse over and over. In order to produce laser outputs, a modulation system is to be used to modulate infrared lasers employed in InfraRed CounterMeasure systems, IRCMs, or Directional InfraRed CounterMeasure systems, DIRCMs.
The infrared laser in these systems must be modulated so that it produces a pulsed output having the desired waveform. For instance, the desired waveform may include long pulses, with short inter pulse spacing; or shortened pulses with long inter pulse spacing; or indeed any combination thereof.
The problem is how to generate the desired pulsed waveforms over ten to twenty seconds; and to do so without significant software intervention or large amounts of rack space in the equipment bay of an aircraft.
In the past, modulators are typically set to generate a relatively short waveform, for instance over 100 milliseconds, and then simply repeat the sequence until the twenty second engagement interval has been completed. However, this type of waveform replication does not effectively countermeasure seekers because the seeker's response can vary over time, requiring different waveforms. There is therefore a need to be able to provide a pulse train that has a pulse width variable waveform that extends over the entire engagement interval and varies to eliminate the effect of varying seeker parameters, be they environmental or intentional.
One brute force approach to the generation of pulsed waveforms is to divide up the waveform into segments or slices and generate the pulse-on pulse-off times for the pulses in each segment or slice utilizing a separate pulse generator. The slices are then chained together to form the desired elongated pulse train. However, it will be appreciated that if one needed a separate piece of equipment for every 100 millisecond time segment, producing twenty seconds worth of waveforms would be prohibitively expensive, not only in terms of cost, but also in terms of rack space.
There is therefore a necessity to provide a miniature waveform modulator that can modulate an infrared laser so as to produce a completely characterized and controllable waveform that has precise pulse widths over an extended period of time, without the use of replication.
In short, there is necessity for a miniature waveform modulator that performs full pulse-by-pulse timing control which not only is capable of characterizing the entire pulse train over twenty seconds but is also capable of high pulse repetition rates in which a narrower variable width pulses can be generated, for instance pulse widths of 500 microseconds, or less.
While one could conceivably produce the desired pulse train utilizing software, the software overhead oftentimes exceeds the inter pulse spacing, thus preventing high repetition rate pulse generation. This is because one could not pulse-on and pulse-off fast enough due to the software overhead.
Moreover, there is a requirement to package a fully programmable and controllable waveform generator in a small compact electronic card so as to occupy virtually no rack space in the equipment bay of an aircraft. One also needs the ability to package a complete laser or lamp sub-system into a single and compact unit by significantly reducing the size of the control electronics. Most important is the capability to precisely control all individual time periods in the entire waveform and to do so over extended periods of time such that the pulses in the pulsed waveform can be provided with different pulse widths over the entire multi-second engagement period.